During drilling operations for the extraction of hydrocarbons, a variety of recording and transmission techniques are used to provide or record real-time data from the vicinity of a drill bit. Measurements of the surrounding subterranean formations may be made throughout drilling operations using downhole measurement and logging tools, such as measurement-while-drilling (MWD) and/or logging-while-drilling (LWD) tools, which help characterize the formations and aid in making operational decisions. Wellbore logging tools make measurements that may be used to determine the electrical resistivity (or its inverse, conductivity) of the formations being penetrated, where the electrical resistivity indicates various features of the formations. Those measurements may be taken using one or more antennas coupled to or otherwise associated with the wellbore logging tools.
Logging tool antennas are often formed by positioning coil windings about an axial section of the logging tool, such as a drill collar. A ferrite material or “ferrites” are sometimes positioned beneath the coil windings to increase the efficiency and/or sensitivity of the antenna. The ferrites facilitate a higher magnetic permeability path (i.e., a flux conduit) for the magnetic field generated by the coil windings, and help shield the coil windings from the drill collar and associated losses (e.g., eddy currents generated on the drill collar).